The present invention relates to certain novel compositions of matter and the method of preparing such compositions which comprises reacting three parts of an organic epoxide with one part of a modified epoxy prepolymer containing a fatty acid.
Epoxy resins are well known in the art, and have matured into sophisticated materials capable of meeting the requirements of new applications. Typical uses for epoxies include protective coatings, adhesives, laminates, potting, castings, compression and transfer molding.
The most common, or conventional epoxy resins are obtained by reacting epichlorohydrin with a polyhydroxyl compound, such as Bisphenol A, in the presence of a catalyst. By varying the ratio of epichlorohydrin to Bisphenol A, resins may be produced which range from low viscosity materials to high melting solids. As the length of the molecule increases, the epoxide value decreases, and the hydroxyl equivalent increases.
The selection of the proper curing agent for a particular application can be determined after considering the end use requirements. Viscosity of the mixture, system working life, curing cycle and the operating environment are some factors to be considered when selecting a curing agent. Generally when an epoxy resin is cured catalytically, the catalyst opens the epoxy group to permit the molecules to co-react with one another. Typical epoxy resin catalysts are short chain amides, tertiary amines, nonfunctional secondary amines and Lewis acid complexes. The catalyst concentration must be determined empirically for each system, and the cured properties of the epoxy vary, depending on the materials employed.
Cross-linking comonomers are coupled directly into the cured system as integral members of the molecular network. These comonomer hardners react with the epoxy group. Typical amine cross-linking agents are diethylenetriamine, triethylenetetramine, aminoethyl piperizines, polyamides and primary aromatic polyamines.
Foamed epoxy resins are also well known in the art. The standard practice in making epoxy resin foams has been to mix the resin with an amine curing agent and a blowing agent at temperatures below the thermal decomposition temperatures of the blowing agent, filling a suitable mold cavity with the mixture and heating the mixture so that the blowing agent decomposes with the evolution of gas and concurrent foam generation, the resin curing to its thermoset condition under the influence of the curing agent. An improvement to this standard practice was taught in U.S. Pat. No. 3,223,654 to Nickerson, et al. wherein a prepolymer of epoxy and a polyamine was reacted with additional epoxy and additional polyamine, which not only cured the epoxy, but provided the exothermic reaction to decompose the blowing agent. An epoxy foam insulation material prepared from an epoxy, siloxane and a polyamineamide, preferably an adduct of the Diels-Alder dimerization of linoleic acid reacted with a polyamine, was taught in U.S. Pat. No. 3,296,153 to Snorgren. Further, U.S. Pat. No. 2,993,014 to Schardt taught that a polyamide, the condensation product of a dimerized fatty acid and a polyamine, would cure an epoxy.
Despite the advances made in the prior art, they failed in one or more ways to produce a gas or air frothable epoxy foam that cured at room temperature in less than an hour, but cured sufficiently slow and that was shear-stable to permit troweling. In none of the referenced prior art was the foam produced by simple whipping-in of air or N.sub.2 using a Hobart or Kitchen-Aid type of mixer similar to that employed for whipping cream or frothing egg whites. Additionally, many compositions in the prior art cured the epoxy in such a short time that it could not be troweled. Other formulations could not be cured at room temperature within a reasonable time while others did not produce a stable foam.
Despite the advances made in the prior art, and the knowledge of how to formulate a specific epoxy system to meet specific requirements, we found, surprisingly, that the incorporation of a fatty acid into a specific epoxy system produced a formulation that could be frothed readily. The thixotropic foam was very stable, and in addition to being poured onto surfaces or into molds could be applied to many sufaces using a trowel or spatula. The system cures at room temperature to produce either a flexible or rigid foam, depending on minor variations in the formulation, that can be used as an adhesive, as insulation, for packaging, or for other applications that might occur to one skilled in the art.